One of the problems encountered with boat trailer tail lights is breakage of the light bulbs
bulbs are contacted by water during launching the heated of the boat. The bulbs may become heated by the continuous illumination of the bulbs during nighttime trailering, or through frequent operation of the brakes during a launching operation. When the heated bulb is contacted by cold water, the bulb may fracture, thus requiring replacement.
In an attempt to overcome this problem, sealed tail lights have been marketed in which the bulbs are contained within a sealed housing. The seal is accomplished by utilizing a resilient gasket between the lenses and the housing. When the light bulbs of the sealed tail light burn out and need replacement, the replacement is normally done by the boat owner. As a result, many times the sealing gaskets are not properly installed when the lenses are reassembled to the housing. Thus, the sealed characteristics are destroyed, enabling water to enter the housing and contact the bulb.
Another approach to the problem of bulb breakage has been to utilize trailer lights which operate on the air entrapment principle, as disclosed in U.S. Pat. Nos. 3,106,349 and 3,858,039. With tail lights of the type shown in U.S. Pat. No. 3,106,349, the upper end of the housing is sealed, while the lower end of the housing is provided with an opening through which water can enter the housing. As the water rises in the housing during launching of the boat, the air is entrapped in the upper end, preventing the water from rising to a level to contact the bulbs or connections. However, problems have arisen with tail lights of this type. The water within the housing may be jostled as the trailer is moved over uneven terrain during launching, causing the water to splash against the bulbs and the connections. If the bulb is heated, the splashing water may break the bulb, and contact with the connections can cause corrosion.
More recently, boat trailer lights have been constructed utilizing a capsule that is contained within the outer housing, as disclosed in U.S. Pat. No. 4,617,617. In submersible tail lights of this type the bulbs are contained within the transparent capsule and the lower end of the capsule is provided with a hole through which water can enter the capsule; but due to the closed upper end, air will be entrapped in the upper end of the capsule to prevent the water from contacting the bulbs.